Abrading machinery



Feb- 20, 1968 c. T. FREERKS ETAL 3,369,328

ABRADING MACHINERY Filed Feb. 8, 1965 United States Patent Otilice 3,369,328 Patented Feb. 20, 1968 3,369,328 ABRADING MACHINERY Conrad T. Freerks, Maplewood, Ralph W. Reed, White Bear Lake Township, Ramsey County, and James E. Whelan, Birchwood, Minn., assignors toMinnesota Mining and Manufacturing CompanySt. Paul, Minn., a corporation of Delaware Filed Feb. 8, 1965, Ser. No. 430,826 4 Claims. (Cl. 51-216) ABSTRACT OF THE DISCLOSURE A knee-activated valve permits infinitely variable pressure control to precisely and quickly adjust the force applied to a workpiece being thrust against a moving abrading means.

This invention relates to abrading machinery and is particularly concerned with an improved workfeed device.

For many years abrading machines have incorporated means to help an operator applying greater pressure to a workpiece than he would be able to with brute strength alone. For example, U.S. Patent 1,422,749 shows an arrangement of springs, pulleys, and levers, whereby a grinding machine operator may 'exert additional force on the workpiece by standing on a lever. Others have employed hydraulic or pneumatic devices to augment the pressure applied to the workpiece; see, eg., U.S. Patent Nos. 1,683,354; 1,713,722; 1,875,486 and 2,686,994. Nevertheless, despite the recognized need in the industry, no one prior to our invention provided a workfeed device which was widely accepted by the abrading machine operators.

The prior art devices employing hydraulic or pneumatic pressure typically provided either full pressure or no pressure at all, leaving the operator no leeway for instantaneous variation of pressure. Further, most of the prior art workfeed devices were designed for use with grinding wheels. Grinding wheels lack resilience, and exceeding the pressure recommended by the manufacturer may cause the wheel to explode. Additionally, all grinding wheels wear substantially in use, thereby making it diicult to maintain precision tolerances. Modern coated abrasive belts overcome many of the drawbacks of grinding wheels, providing a strong-fast-cutting durable abrading means which can be entrained over a contact wheel or a platen and held to quite precise tolerances. Although the device of our invention may be used in connection with any abrading means, it finds particular utility in connection with abrasive belt machines.

In many tests the ,productionl obtained from a given coated abrasive belt using our workfeed device has been increased more than 1000% and in other cases the time for abrading a given number of workpieces has been cut in half, Often the increased rate of stock removal so diminishes the normal conduction of frictional heat to the main body of the workpiece that an operator need not use gloves, which may be drawn into a fastmoving abrading medium. Fast, controlled cutting action also prevents smearing, burning, or distortion of workpieces.

The workfeed device of our invention enables an operator, for the first time so far as we are aware, to use both hands to guide a workpiece while at the same time precisely and continuously controlling the force urging the workpiece against the abrading means. Pressure can be either increased or decreased almost instantaneously, and in the degree desired, whether gross or minute.

An understanding of our invention will be facilitated by referring to the attached drawings, in which like numbers refer to like parts in the several views, and in which:

FIGURE 1 is a view in perspective of a preferred embodiment of our invention;

FIGURE 2 is a rear elevational view of the device of FIGURE 1;

FIGURE 3 is a side elevational view of the device of FIGURE 1, with certain portions broken away to facilitate understanding; and

FIGURE 4 is a cross-sectional view of an infinitely variable quick-operating pressure control valve which plays an important part in our invention.

In the drawings, the device 10 comprises base 11, which may be bolted in a desired location on the door. Extend ing vertically upward from base 11 is column 12, which supports and is surrounded by, at its upper portion, sleeve 13. At the upper end of sleeve 13 is horizontally positioned work table 14, on which is mounted horizontally adjustable block 15. Attached to block 1S is fluid-actuated pressure cylinder 16, within which is mounted piston 17, to the end of which is affixed pusher plate 18. When fluid is supplied to cylinder 16 under pressure, piston 17 is forced outward, and a workpiece W, positioned on the top of table 14, is forced against abrasive belt A, which is entrained over contact wheel C. Workpieces of different size may be accommodated by adjusting block 15 either toward -or away from contact wheel C. Because of the precision available with coated abrasive belts, it is possible to position and maintain table 14 within 1A; inch of abrasive belt A; in fact, the speed of the belt and the pressure we prefer to apply, generally makes this a desirable spacing. l

One of the desirable features of our invention is the constant angle at which a workpiece is forced against the abrading medium, even when piston 17 and pusher plate 18 traverse an extended stroke. The specific conformation of pusher plate 18will, of course, be determined by the shape of workpiece W, and we contemplate the use of a variety of interchangeable pusher plates.

In the device shown, air is supplied through supply line 19, passing through air filter 20, past line pressure gauge 21, and line pressure control valve 22. The air then passes through line oiler 23 and hose 24 to variable pressure control valve 25, entering through inlet 26 and 1eaving through outlet 27. Between outlet 27 and cylinder 16 are included air line 30, containing speed control valve 28 and quick release (or dump) valve 29.` Speed control valve 28 may be adjusted to establish the rate at which pressure changes when variable pressure control valve 25 is actuated, thereby in turn controlling the rate at which the pressure is increased in line 30. Quick releasevalve 29 permits piston 17 to move quickly away from contact wheel C when variable pressure control valve 25 is closed; 4

thus., when pressure is removed from the upstream side of valve 29, the air on the downstream side quickly escapes. Further to facilitate the action of moving piston 17 away from contact wheel C, a coil-spring S, as is particularly shown in the partially cut away portion of FIG- URE 3 may enclose the piston rod of piston 17, being positioned between the head of piston and the forward end of cylinder 16.

In order to permit an operator to use both hands to position workpiece W on table 14 and to adjust it as needed, variable control valve 25 is operated by kneeactuated lever 33, to the outer extremity of which is afxed pad 34. Lever 33 and valve 25 are both adjustable to an appropriate height by means of U-bolt32, which surrounds column 12. When the operator wishes to increase the pressure applied to workpiece W, he moves his knee laterally. Coil-spring 36, positioned between the inner end of lever 33 and valve 25 returns lever 33 to its original position after the pressure has been removed,

'a a and, in a manner to be described, removes all pressure from piston 16.

As noted before, sleeve 13 surrounds column 12 and is vertically adjustable with respect thereto, being held in place by lock handle 38. FIGURES 2 and 3 illustrate a convenient way in which the height of table 14 may be changed, while simultaneously imparting greater stability to the entire assembly. U-bolt 39 surrounds sleeve 13, passing through and firmly holding bar 40. To the outboard ends of bar 40 are attached braces 41 and 41a, which are connected to the oor forward of the assembly. Turnbuckles 42 and 42a connect the separated ends of braces of 41 and 41a respectively. By loosening lock handle 38 and rotating turnbuckles 42 and 42a, the height of the table may be conveniently adjusted. This operation may be further facilitated by surrounding column 12 with a coil spring, the lower end of which bears against, e.g., U-bolt 32, and the upper end of which bears against the under surface of table 14, thereby providing a more or less floating arrangement when lock handle 38 is loosened and turnbuckles 41 and 41a are adjusted.

It is a significant feature of the present invention that an infinitely variable quick-acting pressure control valve is provided. One form of such a valve, devised by Arlie Knutson, is illustrated more fully in FIGURE 4, which will now be discussed in greater detail. Lever 33 is pivoted about pin 37, bolt 35 extending from face 33a of lever 33 and providing the means by which valve 25 is actuated. Valve 25 comprises sub-housing sections 52, 53, and 54. Clamped between sub-housings 52 and 53 is diaphragm 55, in the center of which is flange 56. A tight seal between section 53 and sections 52 and 54 is provided by diaphragm 55 and O-ring 65. Firmly anchored within the hollow central portion of flange 56 is metal diaphragm center 57, in thecentral portion of which is hole S. Poppet valve 61 is positioned within sub-housings 53 and 54, coil-spring 62 serving to urge stem 61a of valve 61 toward hole 58, sealing it under normal operating conditions. Rubber gasket-covered base 67 of valve 61 seats against tubular core 53a of housing 53. All those portions of pressure control valve just described are part of a conventional pressure regulator valve.

Positioned within housing 52, and replacing the normal screw-threaded pressure adjustment device of a conventional pressure regulator valve, is plunger 59, having across the end which contacts metal `center portion 57, a diametric slot 60, which is aligned with hole 58. Bolt in lever face 33a normally bears lightly against the outer end of plunger 59. When the operator exerts lateral force against pad 34, thereby moving the outboard end of lever 33 to his right, the head of bolt 35 is forced against the outer end of plunger 59, which in turn transmits force, through metal center 57 of diaphragm 55, to valve stem 61a of poppet valve 61, thereby forcing seat 67 of poppet valve 61 away from tubular center 53a. O-ring 66 surrounds valve 61, insuring alignment. Normally air under line pressure is admitted at inlet 26, but does not pass beyond the chamber immediately adjacent inlet 26. When, however, valve 67 is moved from its normal seat, air flows from inlet 26 between poppet valve base 67 and its seat on tubular core 53a, through hole 63 and thence through outlet 27. The air then equalizes the pressure on diaphragm by passing through hole 64, thereby applying pneumatic force on theleft side of diaphragm 55 to equalize the mechanical force being applied to Athe right side thereof. To increase the pressure at outlet 27, the operator increases the force applied to knee pad 34, the valve adjusting to the changed conditions in the manner just indicated.

When the operator wishes to decrease the output pressure from valve 25, he decreases the pressure on knee pad 34, thereby withdrawing bolt 35 from contact with plunger 59. The ail pressure on the left side of diaphragm 55 then forces diaphragm 55 to the right; the air escapes through center hole. 58 and escape hole 52a until pressure is reduced to a point where equilibrium is again achieved.

What we claim is:

1. An abrading machine comprising an abrading means and a Workfeed device which comprises in combination: a horizontal table for supporting a workpiece, a block on the upper face of said table adjustably mounted for movement toward and away from said abrading means, a pneumatic cylinder affixed to said block, said cylinder containing a horizontally movable piston having a workpiece-urging pusher plate connected to the external end thereof, a vertically adjustable support for said table, an air line for supplying compressed air to said cylinder, a valve in said air line for either quickly or slowly increasing or decreasing the pressure of air in said cylinder, and, a knee activated control for said infinitely adjustable pressure control valve.

2. The abrading machine of claim 1 wherein the kneeactivated control is aixed to the vertically adjustable support.

3. The abrading machine of claim 2 wherein a quickrelease valve is included in the air line between the valve and the piston.

4. The machine of claim 3 wherein means is connected to the cylinder for moving the piston away from the abrading means in the absence of air pressure.

References Cited UNITED STATES PATENTS 280,033 6/ 1883 Hadley. 1,422,749 7/1922 Dameron 51-98 1,442,041 1/1923 Boddie 51--215 X 1,875,486 9/1932 Peaslee 51-238 2,148,369 2/1939 Eastwood 51-240 X 2,462,788 2/ 1949 Sutton 51-143 2,686,994 8/1954 Wyborski 51-165 LESTER M. SWINGLE, Primary Examiner.

D. G. KELLY, Assistant Examiner. 

